The present invention relates to a positive displacement dry pump, a purge system for such a pump and a method of purging a positive displacement dry pump.
Positive displacement pumps such as roots, claw or rotary vane pumps may comprise a plurality of vacuum pumping stages having respective pumping mechanisms driven by one or more drive shafts. The drive shafts may themselves be driven by respective motors or more usually, one shaft can be driven by a motor whilst a second drive shaft is connected by a gear arrangement to the first drive shaft. Typically, the drive shafts are supported for rotation by bearing arrangements housed in lubrication chambers at the high vacuum side and low vacuum side of the pump.
The drive shafts extend through openings in head plates of the lubrication chambers and the space between the shafts and the head plates are sealed by shaft seals. Although the shaft seals are generally quite effective, leakage of fluid still occurs through the openings dependent upon the relative pressures on each side of the head plates. When pumping certain gasses, it is desirable to resist the passage of the gasses into the lubrication chambers, which degrade the lubricant and can cause damage to the pump's components. It is known to use purge gas to prevent pumped gasses from entering the lubrication chambers and this method is typically adopted at the low vacuum lubrication chamber. However, the introduction of purge gas at the high vacuum side of the pump can limit the pump's ability to generate high vacuum pressures at the pump inlet.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.